1. Field of the Invention
The present invention relates to a variable displacement wobble plate type compressor having a variable angle wobble plate mechanism within a crankcase chamber and a solenoid-operated wobble angle control unit capable of automatically changing a compressor displacement by changing the angle of inclination of the wobble plate mechanism coupled with compressor pistons in response to a change in a cooling load in an air-conditioning system in which the wobble plate type compressor is accommodated. More particularly, it relates to an improvement in the solenoid-operated wobble angle control unit for enhancing the performance of the control unit.
2. Description of the Related Art
A variable displacement wobble plate type compressor employing a solenoid-operated valve for controlling a wobble plate angularity is typically disclosed in U.S. Pat. No. 4,533,299 to Swain et al. In the compressor, the solenoid-operated valve is used for controlling the opening and closing of a passageway between a high pressure discharge chamber and a crankcase chamber in which a variable angle wobble plate mechanism to drive the reciprocating motion of compressor pistons is accommodated. When the passageway between the high pressure discharge chamber and the crankcase chamber is opened, a high pressure gas is permitted to flow from the discharge chamber into the crankcase chamber so that a rise in pressure within the crankcase chamber occurs and a small angularity of the wobble plate mechanism is achieved. On the other hand, in the disclosed compressor, the crankcase chamber is communicated with a low pressure suction chamber of the compressor by another passageway having an orifice permitting a blow-by gas leaking from compressor cylinder bores into the crankcase chamber to escape from the crankcase chamber into the suction chamber. However, due to provision of the orifice, the crankcase chamber is always communicated with the low pressure suction chamber, and as a result, at the initial stage of the opening of the passageway between the high pressure discharge chamber and the crankcase chamber, a high pressure gas flowing from the discharge chamber to the crankcase chamber is able to escape from the crankcase chamber toward the suction chamber, and accordingly, the high pressure gas is unable achieve the desired function of contributing to a smooth and quick rise in the crankcase chamber pressure.
U.S. Pat. No. 4,586,874 to Hiraga et al discloses another variable displacement wobble plate type compressor employing a solenoid-operated valve mechanism for controlling the wobble plate angularity. The solenoid-operated valve mechanism of U.S. Pat. No. 4,586,874 is arranged so as to be capable of opening and closing a passageway between a crankcase chamber and a suction chamber of the compressor. That is, when the passageway is opened by the solenoid-operated valve mechanism, a decrease in pressure within the crankcase chamber occurs so that the angularity of the wobble plate can be increased. However, in the solenoid-operated valve mechanism for controlling the wobble plate angularity of U.S. Pat. No. 4,586,874, an increase in pressure of the crankcase chamber for reducing the wobble plate angularity must rely on a blow-by gas leaking from compressor cylinders into the crankcase chamber during the closing of the solenoid-operated valve plate. Accordingly, in the compressor of U.S. Pat. No. 4,586,874, a high discharge pressure gas is not used for increasing the crankcase chamber pressure and thus it is difficult to realize a smooth and quick change in the wobble plate angularity in response to a change in a cooling load.
U.S. Pat. No. 4,702,677 to Takenaka et al discloses a further variable displacement wobble plate type compressor with a wobble angle return system for promoting a quick return of the wobble plate from the least wobble angle position to a larger wobble angle position. The wobble angle return system employs first and second mechanically operated valves, the first valve being used for controlling fluid communication between a crankcase chamber and a discharge chamber of the compressor, and the second value being used for controlling an extent of fluid communication between the crankcase chamber and a suction chamber of the compressor. However, the wobble angle return system of U.S. Pat. No. 4,702,677 does not teach a complete association of the operation of the first and second valves. Moreover, the system is silent about the employment of a solenoid-operated valve means. Thus, the wobble angle return system of U.S. Pat. No. 4,702,677 has a limitation in the rapidity of a change in the wobble plate angularity.